Key Engineering Materials Vols. 317-318

Abstract: The photocatalytic activity of undoped and ZrO2-doped titania nanocrystals, prepared by a surfactant-assisted templating method (SATM), was investigated based on the formation of tri-iodide (I3 -) species in titania suspension in KI solution under UV-irradiation. Optimum dopant concentration was found to be 0.5mol% ZrO2-doping in titania. The effects of dopant concentrations and gelation conditions (gelation at 80oC, and gelation under hydrothermal treatment) on the photocatalytic activity of the synthesized titania-based nanocrystals are also presented.

Abstract: In the present study, Pt, NiO, and RuO2 fine particles as co-catalyst were loaded on the LiInO2 surface by different methods for enhancing its adsorption capability and photocatalytic activity for methylene blue dye (MB) decomposition. Clear adsorption capability and marked photocatalytic activity for MB decomposition were confirmed on the co-catalyst loaded LiInO2 composite particles. Comparing with that of LiINO2, the previously reported NaInO2 photocatalyst had stronger adsorption capability and higher photocatalytic activity. However, the adsorption capabilities and the photocatalytic activities were separately in the same order of RuO2/AInO2 > Pt/AInO2 > AInO2 > NiO/AInO2 and Pt/LiInO2 > RuO2/LiInO2 > NiO/LiInO2 > LiInO2 for the two promising AInO2 (A = Li+ or Na+) photocatalyst.

Abstract: TiO2 (Vis-TiO2) thin films absorbing UV and visible light in regions of 250-600nm have been successfully developed by applying a radio-frequency (RF) magnetron sputtering deposition method. SIMS depth profiles of Vis-TiO2 revealed that the O/Ti ratio gradually decreases from the top surface (O/Ti ratio : 2.00 ± 0.01) to the inside (1.93 ± 0.01). This unique declined O/Ti composition (anisotropic structure) may be the origin of the significant perturbation in the electronic structure of Vis-TiO2, enabling the absorption of visible light and their high photocatalytic performance under visible light irradiation. In fact, it was found that the separate evolution of H2 and O2 from water could be successfully achieved under visible light or solar light irradiation by applying these thin film photocatalysts in an H-type glass container separating the two aqueous solutions by a TiO2 thin film and proton-exchange membrane, having H2 evolution from Pt side and O2 evolution from TiO2 thin film side, respectively.

Abstract: An innovative Pd-perovskite “Intelligent Catalyst”, which exhibits a greatly improved durability owing to the self-regeneration function of Pd nanoparticles, has been developed. The Pd-perovskite catalyst was prepared by the alkoxide method, and X-ray absorption fine structure (XAFS) measurements were carried out in SPring-8 using the 8-GeV synchrotron radiation. Pd occupied the B-site (6-fold coordination) of the perovskite lattice in the oxidative atmosphere, and segregated out to form metallic nanoparticles in the reductive atmosphere. The catalyst retained a predominantly perovskite structure throughout a redox cycle of the exhaust-gas, while the local structure around Pd could be changed in a completely reversible manner. The agglomeration and growth of the metal particles is suppressed as a result of the Pd movement between inside and outside the perovskite lattice. This function enables an automotive catalyst to regenerate itself into an active state in fluctuation typically encountered in the exhaust gas from the gasoline engine. And it is revealed, by in-situ and ex-situ XAFS analyses, that the self-regenerative function of Pd occurred in a wide temperature range from very low to high one. The intelligent catalyst is one solution for precious metals supply and demand problem, and is expected to become the global standard of the catalyst technology.

Abstract: Co-free LaFePdO3 perovskite catalyst with the self-regenerative function of Pd was developed. This technology was named the “intelligent catalyst”. Suppression capacity for Pd particle growth and catalytic activity of the Co-free perovskite LaFePdO3 were compared with those of LaFeCoPdO3. It was confirmed that Pd particles on LaFePdO3 maintained a nano-particle size by the results of XAFS analysis and TEM observation after aging in engine exhaust gas at 900 °C, and LaFePdO3 demonstrated an excellent light-off performance. Further, the design configuration for LaFePdO3 in the washcoat was investigated to maximize the self-regenerative function under practical conditions.

Abstract: ZnO nanopowder was prepared by a novel “solution-combustion method (SCM)” and it was used as a semiconductor photocatalyst to evaluate its photoreduction properties. Aqueous Pb-EDTA and Cu-EDTA solutions of heavy metal ions (Pb and Cu) were used for the photocatalysis reaction under UV illumination. The result was then compared with other semiconductor photocatalyst powder such as TiO2 powder (P25; Degussa) and TiO2 powder prepared by homogeneous precipitation process at low temperature (HPPLT). In the removal of Pb++ ions, the ZnO nanopowder showed 2.6 fold higher removal rate than P25 TiO2 powder and 1.8 fold higher than HPPLT TiO2. Also the ZnO nanopowder showed the highest removal rate of the Cu++ ions from the solution among the different photocatalyst powders compared. The superior photoreduction ability of the ZnO nanopowder appears to be due to its excellent UV absorption characteristics. This was confirmed by the photoluminescence (PL) measurement.

Abstract: Photocatlytic ZnO nanopowders were synthesized by a novel method referred to as “solution-combustion method (SCM)”. They were synthesized using various oxidants and fuels. Single-phase ZnO powders were obtained. The ZnO powder synthesized using Zn(OH)2 and glycine as an oxidant and a fuel at fuel/oxidant ratio of 0.8, showed best powder characteristics such as average grain size of 30 nm and the specific surface area of 120 m2/g. The photocatalytic gold recovery efficiency by this SCM ZnO nanopowders was about 6 fold higher compared to the case by the state of the art commercial TiO2 nanopowders. The purity of recovered gold was about 99.6% in weight% and 98.8% in atomic%. Especially, in this study it was tried to recover gold metal ions from not simulated wastewater but real plating one. This technology is therefore very viable and cost-effective to obtain high purity gold from plating wastewater.

Abstract: The effects of sintering additives on dielectric loss tangent of AlN ceramics were explored. Different amounts of Y2O3 and TiO2 were respectively added as sintering additives to AlN powders and pressureless sintering was performed in a nitrogen flow atmosphere at 1850 °C or 1900 °C for 2 hours. The resulted AlN ceramics became denser when TiO2 addition was more than 0.5 mol%, and a dense sinter with a relative density of 0.987 could be obtained. Tan δ decreased when TiO2 content was more than 0.5 mol% and a tan δ value of as low as 1.0 x 10-3 could be attained.

Abstract: xPb(Ni1/3Nb2/3)O3-yPb(Mn1/3Nb1/3Sb1/3)O3-(1-x-y)Pb(Zr0.48Ti0.52)O3 ceramics have been prepared by a columbite two-step method. NiNb2O6, MnNb2O6 and MnSb2O6 were used as precursors to produce the pseudoquintnary system ceramics. X-ray diffraction (XRD) results indicate that the pseudoquintnary system ceramics have a single-phase perovskite structure. The piezoelectric and dielectric properties of the ceramics were investigated as functions of x or y. The addition of Pb(Ni1/3Nb2/3)O3 makes the piezoelectric properties
to become ‘soft’, while the addition of Pb(Mn1/3Nb1/3Sb1/3)O3 makes the piezoelectric properties to be ‘hard’. The Curie temperature (Tc) of the pseudoquintnary system decreases with the increase of Pb(Ni1/3Nb2/3)O3 or Pb(Mn1/3Nb1/3Sb1/3)O3 contents. The preferred piezoelectric properties were obtained in the composition with x=0.06 and y=0.06.

Abstract: Structures, ferroelectric and piezoelectric properties of (Na0.5Bi0.5)0.90Ba0.10TiO3 ceramic sintered at different temperatures were investigated. The results confirm an important role of sintering temperature on the structure and electrical properties of the ceramic. It was found that the increase of sintering temperature in the range of 1110-1160
promoted the development of crystal structure and microstructural densification, leading to an improvement in ferroelectric properties, poling process and piezoelectric properties. Further increase of the sintering temperature above 1160
resulted in a slight deformation of ceramic specimens. With respect to sintering behavior and piezoelectric properties, a relatively narrow sintering temperature range near 1150
was ascertained to be preferred for the ceramic.